I will try to adapt my code to do 3 at a time for each call.
But I don't know how to achieve that... Could I get a call example?

Lets say I want verts 1,2,34... how would I build the new get_vertex() call?

Currently I would do it like this:
c1= ent_getvertex(Terrain,NULL,1);
c1= ent_getvertex(Terrain,NULL,2);
c1= ent_getvertex(Terrain,NULL,34);